1. Field of the Invention
The present invention relates to an optical information recording medium for recording/reproducing information by irradiation of laser light, and further relates to a method and an apparatus for recording/reproducing information on this medium.
2. Description of the Prior Art
Optical information media have been noted widely as a large capacity and high density memory, and erasable media that can be rewritten have been under development at present. In one of the erasable optical information recording media, a recording layer made of a phase change material that changes between an amorphous state and a crystalline state is formed on a substrate, and information is recorded and erased by irradiating the recording layer with laser light.
An alloy film comprising Ge, Sb, Te, or In as the main components such as a GeSbTe alloy is known as a phase change material for the recording layer. Information is recorded by making the recording layer partially amorphous to form recording marks. The recording layer is made amorphous by heating the recording layer to the melting point or more and cooling it. The recording layer is made crystalline by heating the recording layer to the crystallization temperature or more and not more than the melting point. The reflectance and the transmittance of the irradiated laser light in a region in which a recording mark is formed are different from those in other regions.
In general, spiral or concentric circular guide grooves that are tracked by laser light for recording/reproducing information previously are provided on a substrate. Regions between the grooves are called lands. In recordable CDs (CD-R) or minidisks (MD), either grooves or lands are used as information tracks to record information on, and the other is used as a guard band for separating adjacent information tracks.
In recent years, with improvement of the processing ability of various information equipment, the amount of information to be handled has increased. For this reason, there is a great demand for recording media with a larger capacity than ever. As one approach to achieve larger capacity, in DVD-RAMs or the like, a method for increasing track density by recording information on both grooves and lands is adopted (land and groove recording method).
In DVD-RAMs, a format structure called a ZCLV (Zoned Constant Liner Velocity) method is adopted. In this format structure, an information track is segmented into a large number of information recording regions (sectors) by addresses indicating the position on the medium. Further, several information recording regions are grouped in the radial direction to form a zone. The number of sectors corresponding to one rotation and the rotation speed are increased step by step by each zone from the inner circumference to the outer circumference. In each zone, the rotation speed is constant, and the linear velocity and the duration of a sector are substantially constant between the zones.
On the other hand, in CD-Rs or MDs, a CLV (Constant Liner Velocity) method is used in which information is recorded/reproduced at a constant linear velocity throughout the recording regions. This method can achieve the maximum recording density, and has an advantage in that the design of the recording layer is easy because the thermal conditions during recording are constant.
In the CLV method, it is necessary to change the rotation speed frequently for random access. For this change, the grooves are wobbled in the radial direction at a constant spatial frequency, and a rotating motor of a recording/reproducing apparatus is controlled based on signals obtained from these wobbles for recording/reproducing information. However, the length of a groove for one rotation is varied with the position in the radial direction, so that a phase difference occurs between the wobbles in the adjacent grooves. Therefore, when the land and groove recording method is used with the CLV method, signals are synthesized from wobbles having different phases in the land portion. Thus, good circuit control signals cannot be obtained.
In order to solve this problem, JP 6-338066 has proposed a recording medium in which only one edge of a groove is wobbled. In this recording medium, address information is recorded as a signal that has been frequency-modulated, using a rotation control signal as the carrier frequency.
However, when a gap between information tracks (track pitch) is narrowed to achieve higher density, the ratio of the variation of the information track width is increased, if the amplitude of the wobble is unchanged. Therefore, the signal amplitude is varied during reproduction of information, so that signal quality is deteriorated. On the other hand, when the amplitude of the wobble is reduced as well, the intensity of the signal obtained from the wobble is reduced, which makes it difficult to detect address information.
Furthermore, as another approach to achieve higher density information recording, multilayered recording media including at least two recording layers are proposed. In many multilayered recording media, it is necessary to record/reproduce information with laser light that has passed through another recording layer. Furthermore, it may be necessary to record information successively on a plurality of recording layers, or reproduce information continuously from a plurality of recording layers.
Therefore, with the foregoing in mind, it is an object of the present invention to provide an optical information recording medium with a large capacity that can achieve easy and reliable recording/reproduction of information. More specifically, first, it is an object of the present invention to provide an optical information recording medium that can achieve easy detection of address information while using the land and groove recording method and the CLV method. Secondly, it is another object of the present invention to provide an optical information recording medium that allows stable recording/reproduction of information even when the recording medium includes two or more recording layers, and information is recorded/reproduced on/from a recording layer with laser light that has passed through another recording layer. Thirdly, it is another object of the present invention to provide an optical information recording medium that can achieve efficient and reliable recording/reproduction of information even when information is recorded/reproduced successively and continuously on/from a plurality of recording layers.
A first optical information recording medium of the present invention includes a disk-shaped transparent substrate and a recording layer for recording, reproducing or erasing information by irradiation of laser light. The recording layer is formed over the substrate, wherein the recording layer comprises information tracks including groove tracks and land tracks that are formed alternately in a radial direction of the disk. The information tracks comprise information recording regions and address regions interposed between the information recording regions. The information recording regions and the address regions are arranged along the tracking direction of the laser light. In the information recording regions, every second step in the radial direction of steps for dividing the groove tracks from the land tracks adjacent to the groove tracks is wobbled in the tracking direction, and in a range whose ends are defined by the address regions the every second step is wobbled at a constant frequency, and prepit addresses for providing information on a position on the recording medium are formed in the address regions.
The first recording medium of the present invention makes it possible to detect the address information reliably when the CLV method is used together with the land and groove method, so that the present invention allows stable recording/reproduction of information.
The present invention also provides a method for recording/reproducing information on the first optical information recording. In this method, information is recorded, reproduced or erased at a constant linear velocity in all the information recording regions while controlling a rotation speed of the recording medium with a rotation control signal obtained from the wobbled steps.
One embodiment of a second optical information recording medium of the present invention includes n recording layers (where n is an integer of at least 2), wherein the recording layers comprise information tracks. The information tracks comprise information recording regions and address regions interposed between the information recording regions. The information recording regions and the address regions are arranged along the tracking direction of the laser light. Prepit addresses for providing information on a position on the recording medium are formed on the address regions, and in at least the first recording layer to the (nxe2x88x921)th recording layer from the transparent substrate side, no pair of adjacent address regions in the radial direction of the disk are arranged so as to be aligned on a straight line passing through the center of the disk.
Another embodiment of the second optical information recording medium includes a disk-shaped transparent substrate and n recording layers (where n is an integer of at least 2) for recording, reproducing or erasing information by irradiation of laser light. The recording layer is formed over the substrate, wherein the recording layers comprise information tracks including groove tracks and land tracks that are formed alternately in a radial direction of the disk. The information tracks comprise information recording regions and address regions interposed between the information recording regions. The information recording regions and the address regions are arranged along the tracking direction of the laser light. Prepit addresses for providing information on a position on the recording medium are formed on the address regions. A pair of adjacent information tracks in the radial direction of the disk have a common address region on which a common prepit address is formed, and in at least the first recording layer to the (nxe2x88x921)th recording layer from the transparent substrate side, no pair of adjacent common address regions in the radial direction are arranged so as to be aligned on a straight line passing through the center of the disk.
The second recording medium allows stable recording/reproduction of information, even when information is recorded/reproduced with laser light that has passed through another recording layer. In this medium, even if the transmittance of the laser light is different between the information recording regions and the address regions, the address regions do not form a block but are dispersed. Therefore, transmitted laser light hardly affects the recording layer. The difference in the transmittance of the laser light is made typically by formation of recording marks on the information recording regions.
The present invention also provides a method and an apparatus for recording/reproducing information suitable for the second optical information recording medium. This method is a recording/reproducing method for an optical information recording medium for recording, reproducing or erasing information by irradiating an optical information recording medium with laser light, including detecting reflected light obtained by irradiating the recording medium with the laser light by a photodetector including two light-receiving portions divided in a direction corresponding to a tracking direction of the laser light; generating a sum signal and a difference signal of electrical signals output from the two light-receiving portions; generating a corrected sum signal obtained by correcting an amplitude variation of the sum signal with the difference signal; and generating data information from the corrected sum signal, thereby reproducing the information.
Furthermore, this apparatus is a recording/reproducing apparatus for an optical information recording medium for recording, reproducing or erasing information by irradiating an optical information recording medium with laser light, including an optical head for outputting reproduction signals of the information based on reflected light obtained by irradiating the recording medium with the laser light. The optical head includes a photodetector including two light-receiving portions divided in a direction corresponding to a tracking direction of the laser light; an addition amplifier for generating a sum signal of electrical signals output from the two light-receiving portions; a differential amplifier for generating a difference signal of electrical signals output from the two light-receiving portions; a waveform correcting circuit for generating a corrected sum signal obtained by correcting an amplitude variation of the sum signal with the difference signal; and a data demodulating circuit for reproducing the information by generating data information from the corrected sum signal.
The above-described recording/reproducing method and apparatus are effective for an optical information recording medium in which no pair of adjacent address regions or adjacent common address regions are formed so as to be aligned on a straight line passing through the center of the disk, such as the second optical information recording medium of the present invention, regardless of the number of the recording layers.
A third optical information recording medium of the present invention includes a disk-shaped transparent substrate and n recording layers (where n is an integer of at least 2) for recording, reproducing or erasing information by irradiation of laser light. The recording layers are formed over the substrate, and include a first recording layer and a second recording layer, the first recording layer including a first information track for guiding the laser light from an inner disk circumference side to an outer disk circumference side by rotation of the disk in a predetermined direction, and the second recording layer including a second information track for guiding the laser light from an outer disk circumference side to an inner disk circumference side by rotation of the disk in the predetermined direction.
The present invention also provides a method for recording/reproducing information on the third optical information recording medium. This method is a method for recording, reproducing or erasing information by irradiating the third optical information recording medium with laser light, wherein when in either one recording layer selected from the first recording layer and the second recording layer, recording, reproducing or erasing information on either one information track selected from the first information track and the second information track ends at either one end selected from an inner circumferential end and an outer circumferential end of the one information track, subsequently in the other recording layer, recording, reproducing or erasing information is performed in succession from the corresponding end in the other track.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.